This invention relates to thermoplastic elastomers comprising at least one silicone ionomer. Ionomers as defined herein are polymers in which the bulk properties are governed by ionic interactions in discrete regions of the material (i.e., ionic aggregates). These predominantly nonpolar macromolecules contain ionic groups as part of the chain, usually at levels less than 15 mol %. Broad literature exists on organic ionomers. Phase segregation of the ionic groups from the bulk of the polymer results in the formation of a second phase, termed ionomeric aggregates. A combination of the difference in solubility parameter between the ionic and siloxane phase and the strong ionic and coordinate bonding formed accounts for the formation of these aggregates.
According to the Eisenberg-Hird-Moore (EHM) model, the ionomeric aggregates occupy a region of about 6 Å and affect a region of about 30 Å resulting in a state of reduced polymer mobility. The small size of these ionomeric aggregates (less then the wavelength of light) ensures the transparency of these materials. The aggregation of ionic groups, also termed “multiplets”, can impart physical crosslinks to the base polymer, greatly modifying the viscoelastic properties of the resulting polymer. In addition, since the crosslinks are physical crosslinks they may be broken up by heating or dissolution and therefore the materials they form may be recycled and/or reformed.
Generally, silicone polymers can form either thermoset or thermoplastic elastomers. With a thermoset elastomer, the silicone polymers are chemically crosslinked. These types of crosslinks are not reversible and therefore thermoset elastomers are not recyclable. Thermoplastic elastomers are polymeric materials which possess both plastic and rubbery properties. Thermoplastic elastomers can be processed using conventional polymer processing methods like extrusion, blow molding, melt spinning, etc. which are challenging for thermosetting systems. They have elastomeric mechanical properties but, unlike conventional thermoset rubbers, they can also be re-processed at elevated temperatures. This re-processability is a major advantage of thermoplastic elastomers over chemically crosslinked rubbers since it allows recycling of fabricated parts and results in a considerable reduction of scrap. With the increased focus on the environment it is very important to develop materials that can be recycled and/or reprocessed when no longer needed.